It said that it was issuing figures without fair value calculations in its business performance numbers in order to provide readers 'with a clear and consistent presentation of the underlying operating performance of the group's ongoing businesses'.

The group's long-term gas sales contracts, commodity instruments relating to its gas holdings and other derivatives contracts were 'significantly affected' by the demands of IAS39.

BG disclosed that it had suffered a £576m swing in the value of its commodity-based contracts under IFRS. 'For the full year, a charge of £172m in respect of re-measurements is included within revenue and other operating income (2006: £404m credit).

'The difference between current market price and the settled sales price of the contracts, BG's price exposures in respect of gas sales commitments and some of its financial instruments - all required by IAS39 - were stripped out of BG's business performance figures and recognised separately as 'disposals re-measurements and impairments.'